Closing the Brief Case: An Unusual Cause of Infective Endocarditis after a Urological Procedure

ANSWERS TO SELF-ASSESSMENT QUESTIONS

1. What is the usual habitat of Actinotignum schaalii?

   1. The digestive tract
   2. The oropharynx
   3. The skin
   4. The genitourinary tract

   Answer: D. A. schaalii is part of the urinary microbiota, predominantly colonizing elderly patients and young children. Interestingly, A. schaalii has not been reported as being a part of the intestinal microbiota.

2. Actinotignum schaalii grows easily under what conditions?

   1. On MacConkey agar under aerobic conditions
   2. On MacConkey agar under conditions of a 5% CO₂ atmosphere
   3. On Trypticase soy agar with 5% sheep blood under aerobic conditions
   4. On Trypticase soy agar with 5% sheep blood under conditions of a 5% CO₂ atmosphere

   Answer: D. The growth of A. schaalii is slow (requiring >48 h) and necessitates the use of blood-enriched media incubated under 5% CO₂ conditions or in anaerobic atmosphere. MacConkey agar, selective for Gram-negative pathogens, is not adapted for use with this Gram-positive organism. Microbiologists should always consider the possibility of the presence of A. schaalii infection in young or elderly patients with leukocyturia when standard chromogenic media remain sterile after 24 h of incubation. In such cases, if urine has been stored in tubes with preservative for no more than 48 h, blood agar plates should be inoculated and incubated at 37°C under 5% CO₂ conditions and/or anaerobically for 48 h.

3. Actinotignum schaalii is usually susceptible to what antibiotic?

   1. Amoxicillin
   2. Co-trimoxazole
   3. Ciprofloxacin
   4. Amdinocillin

Answer: A. A. schaalii is susceptible to all β-lactams except amdinocillin, to which it has been reported to be either susceptible or resistant. It is frequently resistant to co-trimoxazole and to quinolones (norfloxacin and ciprofloxacin). Resistance to these antibiotics, widely used in the treatment of UTIs, is problematic and often results in recurrences.

TAKE HOME POINTS

• Actinotignum schaalii (formerly Actinobaculum schaalii) is an emerging uropathogen.

• A. schaalii can be responsible for invasive infections (bacteremia, endocarditis, spondylodiscitis) and for abscesses.

• A. schaalii infection should be suspected especially in elderly patients and in young children with urinary tract abnormalities or after urological interventions.

• The use of blood agar media incubated 48 h under 5% CO₂ conditions or in anaerobiosis is warranted to detect the presence of A. schaalii in clinical specimens.

• A. schaalii is frequently resistant to co-trimoxazole and fluoroquinolones.

• In cases of A. schaalii-related infections, antibiotic therapy needs to be continued for up to 2 weeks or more depending on the infection site.

See https://doi.org/10.1128/JCM.01400-17 in this issue for case presentation and discussion.